The manufacture of battery separators from a sintered resin is well established in the art. One method of making such separators is disclosed and described in U.S. Pat. No. 3,450,571.
Briefly, such processes involve depositing a powdered heat-fusible resin material such as polyvinyl chloride, polyethylene, polypropylene or similar polymers, copolymers or mixtures thereof onto a conveyor, passing the powdered material through a forming die to form ribs thereon, passing the material through a sintering oven to fuse the resin material into a porous web, and cutting the porous web into battery separators.
Such separators have been commercially successful for a number of years. Recently, however, battery manufacturers have commenced employing a new process for manufacturing dry charge batteries which has lead to some problems with these types of sintered separators. Briefly, this problem arises due to the practice of the battery manufacturers to fill a newly manufactured battery with battery acid, and then removing the battery acid without drying. Such a process leaves the separator and plates in a damp condition which permits current to flow between the plates, thereby self-discharging the battery. In addition, when the pH in the battery reaches about 5-6, certain lead compounds that are formed become soluble and the grids corrode, causing the plates to rapidly deteriorate.